1. Field of the Invention
The present invention relates generally to cutting of sheet material and, more particularly, to trimming or slitting of metallic and nonmetallic sheet material, such as aluminum or plastic sheet material, and, even more particularly, relates to a method and apparatus for improving cut edge quality in trimmed sheet material.
2. Description of Related Art
Side or edge trimming and slitting are common processes practiced in flat rolled products (FRP) production facilities. Such trimming and slitting applications or processes include hot line edge trimming, cold mill edge trimming, and side trimming and slitting. These types of processes are generally required for both ingot source products and continuous cast products.
A major concern in the foregoing types of processes is cut edge quality. In the case of trimming or slitting of metal sheet, it is desirable to reduce burrs, fines, debris, and slivers at the cut edge of the metal sheet. The ideal cut edge should be smooth, free of edge waves (i.e., edge buckles), be clean and free from debris (i.e., fines and slivers), and be burr-free. In most cases, high burr is an indication of poor edge quality. Burr may be generally defined as the material deformed out of the sheet or web plane, which is caused during the cutting process. High burr in the cut, trimmed, or slit metal sheet, for example, can affect downstream winding quality. High burr is often unacceptable to end-use customers, such as automotive, aerospace, and rigid packaging, because high burr metal sheet is problematic in their manufacturing processes.
In general, side or edge trimming and slitting operations incorporate either disk-type knives or block-type knives. Disk-type knives are commonly used in edge trimming and slitting operations involving can body sheets, end stock sheets, lithographic sheets, and other light gauge metal sheets and foil products. Block-type knives are commonly used in hot line edge trimming of metal slabs, cold mill edge trimming of metal sheet, and edge trimming and slitting of medium and medium to heavy gauge metal sheet. In addition to the edge quality issues discussed hereinabove, other important considerations in edge trimming and slitting processes are knife life, knife setup time, and knife changeover time.
Attempts have been made in the prior art to improve both cut edge quality and knife life and performance in the cutting of sheet material, typically metal sheet. One such example is found in U.S. Pat. No. 4,614,142 to Fritz et al., which is incorporated herein by reference. This reference discloses circular cutting shears for longitudinal edging of metal plates and sheets. The cutting shears include upper and lower circular cutters. The upper cutter is inclined towards the surface of the plate or sheet passing between the upper and lower cutters. The upper cutter generally forms an acute angle with the surface of the plate or sheet being cut. In particular, the upper cutter defines a positive rake angle, as defined hereinafter, with respect to the lower cutter. The arrangement of the upper and lower cutters insures that the top cutter runs free from the cut edge of the plate or sheet and that the edges of the cut plate or sheet are spread apart.
U.S. Pat. No. 5,820,999 to Li et al. discloses a method and apparatus for reducing or eliminating sliver formation during aluminum sheet trimming operations for aluminum sheet destined for use in motor vehicles. In general, this reference discloses orienting the aluminum sheet at a cutting angle of at least about 10° with respect to a cutting blade. The cutting angle is measured from a plane generally perpendicular to a cutting direction of the cutting blade. The apparatus and method disclosed in the Li et al. patent cuts the aluminum sheet in discreet trimming operations. The aluminum sheet is not trimmed in a continuous process. The Li et al. patent is incorporated herein by reference. A similar apparatus and method to that disclosed in the Li et al. patent is found in United States Patent Application Publication No. U.S. 2002/0017173, which is also incorporated herein by reference.
In view of the foregoing, a need continues to exist to improve cut edge quality, particularly in edge or side trimming or slitting operations in FRP plants. In addition to improved edge quality, a need exists to improve knife-life and performance in such edge trimming or slitting operations. In particular, a need exists to improve cut edge quality in side trimming or slitting operations involving metal sheet, such as aluminum sheet. Moreover, a need exists to provide a trimming/slitting apparatus and process that is more robust than prior art apparatuses and process, allowing increased clearance between the upper and lower cutters and the use of duller cutting blades or edges.